In the power generation where solar energy such as photovoltaic power generation or solar thermal power generation is utilized, the generated power output is affected by a sunshine condition of the day to significantly fluctuate. For example, power cannot be generated during night-time, and generated power output significantly decreases in a rainy or cloudy day. Also, generated power output significantly fluctuates in a day in a sunshine condition from dawn to dusk or in a sunshine condition when it is clear and cloudy later.
In addition, in the wind power generation where a windmill is used, the generated power output significantly fluctuates according to changes of the wind direction or wind force of the day. In a power generation facility such as a wind farm with a group of windmills, power outputs generated by the respective windmills are added up and thereby the power generation fluctuation in a short period of time can be smoothed; however, the generated power output as a whole cannot be prevented from fluctuating.
A storage cell configured to, when power is excessively generated, store electricity and compensate for power shortage with the electricity is representative of the techniques to smooth or level such fluctuating and unstable generated power output. Chemical batteries such as sodium-sulfur batteries, redox flow batteries, lithium batteries, and lead batteries are known as examples of the storage battery. Any of the chemical batteries cannot absorb power beyond their capacities. Also, if the chemical batteries are fully charged to their capacities, the chemical batteries rapidly deteriorate. Therefore, some of the chemical batteries are regulated such that 80% to 90% of the capacity is set as an upper limit. The output by renewable energy such as solar light or wind power can be predicted to some extent but depends on natural phenomena. Therefore, the output generated beyond prediction cannot be prevented. In such a case, the storage battery may not perform the smoothing function, and if power cannot be supplied to a system, a photovoltaic power or wind power facility is disconnected from the system.
Currently, the storage battery is most typical as equipment for smoothing. However, the technology referred to as compressed air energy storage (CAES) is known as another piece of equipment for smoothing. CAES is configured to store, in place of electricity, compressed air discharged from a compressor when power is excessively generated and to reconvert the compressed air to electricity by an air turbine generator or the like when needed.
Typical prior arts in which this CAES technology is utilized are disclosed in Patent Documents 1 to 3.